1. Field of the Invention
The present invention relates generally to apparatus and methods for treating atherosclerotic disease. In a particular embodiment, the present invention provides a combination of controlled cryogenic cooling and balloon distention of a diseased vessel wall.
A number of percutaneous intravascular procedures have been developed for treating atherosclerotic disease in a patient""s vasculature. The most successful of these treatments is percutaneous transluminal angioplasty (PTA). PTA employs a catheter having an expansible distal end (usually in the form of an inflatable balloon) to dilate a stenotic region in the vasculature to restore adequate blood flow beyond the stenosis. Other procedures for opening stenotic regions include directional arthrectomy, rotational arthrectomy, laser angioplasty, stenting, and the like. While these procedures have gained wide acceptance (either alone or in combination, particularly PTA in combination with stenting), they continue to suffer from significant disadvantages. A particularly common disadvantage with PTA and other known procedures for opening stenotic regions is the subsequent occurrence of restenosis.
Restenosis refers to the re-narrowing of an artery following an initially successful angioplasty or other primary treatment. Restenosis typically occurs within weeks or months of the primary procedure, and may affect up to 50% of all angioplasty patients to some extent. Restenosis results at least in part from smooth muscle cell proliferation in response to the injury caused by the primary treatment. This cell proliferation is referred to as xe2x80x9chyperplasia.xe2x80x9d Blood vessels in which significant restenosis occurs will typically require further treatment.
A number of strategies have been proposed to treat hyperplasia and reduce restenosis. Previously proposed strategies include prolonged balloon inflation, treatment of the blood vessel with a heated balloon, treatment of the blood vessel with radiation, the administration of anti-thrombotic drugs following the primary treatment, stenting of the region following the primary treatment, and the like. While these proposals have enjoyed varying levels of success, no one of these procedures is proven to be entirely successful in avoiding all occurrences of restenosis and hyperplasia.
It has recently been proposed to prevent or slow reclosure of a lesion following angioplasty by remodeling the lesion using a combination of dilation and cryogenic cooling. Co-pending U.S. patent application Ser. No. 09/203,011, filed Dec. 1, 1998 (Attorney Docket No. 18468-000110), the full disclosure of which is incorporated herein by reference, describes an exemplary structure and method for inhibiting restenosis using a cryogenically cooled balloon. While these proposals appear promising, the described structures and methods for carrying out endovascular cryogenic cooling would benefit from still further improvements. For example, the mechanical strength of the vasculature generally requires quite a high pressure to dilate the vessel during conventional angioplasty. Conventional angioplasty often involves the inflation of an angioplasty balloon with a pressure of roughly 10 bar. These relatively high pressures can be safely used within the body when balloons are inflated with a benign liquid such as contrast or saline. However, high pressures involve some risk of significant injury should the balloon fail to contain a cryogenic gas or liquid/gas combination at these high pressures. Additionally, work in connection with the present invention has shown that the antiproliferative efficacy of endoluminal cryogenic systems can be quite sensitive to the temperature to which the tissues are cooled: although commercially available, cryogenic cooling fluids show great promise for endovascular use, it can be challenging to reproducibly effect controlled cooling without having to resort to complex, high pressure, tight tolerance, and/or expensive cryogenic control components.
For these reasons, it would be desirable to provide improved devices, system, and methods for treatment of diseased blood vessels. It would be further desirable if these improved techniques were compatible with known methods for treating atherosclerotic disease, but reduced the occurrence and/or extent of restenosis due to hyperplasia. It would be particularly desirable if these improved techniques were capable of delivering treatment in a very safe and controlled manner so as to avoid injury to adjacent tissues. These devices, systems, and methods should ideally also inhibit hyperplasia and/or neoplasia in the target tissue with minimum side effects, and without requiring a complex control system or making a physician introduce numerous different treatment structures into the target area. At least some of these objections will be met by the invention described hereinafter.
2. Description of the Background Art
A cryoplasty device and method are described in WO 98/38934. Balloon catheters for intravascular cooling or heating of a patient are described in U.S. Pat. No. 5,486,208 and WO 91/05528. A cryosurgical probe with an inflatable bladder for performing intrauterine ablation is described in U.S. Pat. No. 5,501,681. Cryosurgical probes relying on Joule-Thomson cooling are described in U.S. Pat. Nos. 5,275,595; 5,190,539; 5,147,355; 5,078,713; and 3,901,241. Catheters with heated balloons for post-angioplasty and other treatments are described in U.S. Pat. Nos. 5,196,024; 5,191,883; 5,151,100; 5,106,360; 5,092,841; 5,041,089; 5,019,075; and 4,754,752. Cryogenic fluid sources are described in U.S. Pat. Nos. 5,644,502; 5,617,739; and 4,336,691. The following U.S. Patents may also be relevant to the present invention: U.S. Pat. Nos. 5,458,612; 5,545,195; and 5,733,280.
The full disclosures of each of the above U.S. patents are incorporated by reference.
The present invention provides new techniques for treating atherosclerotic disease using controlled cryogenic cooling. The invention may be used as a combination cryogenic/angioplasty catheter, eliminating any need for an exchange procedure to be preformed between dilation of a stenotic region within a vessel wall and the application of cryogenic cooling to inhibit hyperplasia. The cooling catheter may be suitable for cooling the diseased blood vessel before, during, and/or after dilation. Advantageously, controlled cooling of the vessel wall changes its mechanical properties so as to enhance the ease of concurrent and/or subsequent dilation. Cooling and tissue temperatures can be accurately controlled by transferring heat from the vessel wall to a cryogenic fluid through a fluid having a predetermined phase change temperature. The change in phase of this heat-transfer fluid can repeatably limit the cooling catheter (and tissue) to a minimum treatment temperature. The use of a rigid heat exchanger within the dilation balloon enhances containment (and safety) of the cryogenic system.
In a first aspect, the invention provides a temperature-controlled cryogenic surgical system comprising a shaft having a proximal end and a distal end. A heat exchanger is disposed near the distal end of the shaft. A cryogenic fluid supply is in fluid communication with the heat exchanger. Fluid is disposed between the heat exchanger and a tissue engaging surface so as to limit heat transfer therebetween.
Typically, the fluid limits cooling of the tissue engaging surface by changing phase at a predetermined temperature. For example, the fluid may comprise saline having a salinity in the range from about 6% to about 18%, providing a treatment temperature in a range from about xe2x88x925xc2x0 C. to about xe2x88x9215xc2x0 C. In the exemplary embodiment, the tissue engaging surface comprises an outer surface of a balloon, and the saline solution is used to inflate the balloon and limit a minimum tissue temperature using the latent heat of freezing, as the partially frozen saline within the balloon will remain substantially uniformly at the freezing temperature until completely frozen.
In another aspect, the invention provides a temperature-controlled cryogenic surgical catheter for use in a blood vessel of a patient body. The catheter comprises a flexible catheter body having a proximal end and a distal end. The body contains a cryogenic fluid supply lumen, an exhaust lumen, and a balloon inflation lumen. An inexpansible heat exchanger tube is disposed near the distal end of the body in fluid communication with the cryogenic fluid supply lumen and the exhaust lumen. A balloon containing the heat exchanger is in fluid communication with the inflation lumen, the balloon having a balloon wall. A balloon inflation fluid having a predetermined phase change temperature is disposed within the balloon between the heat exchanger and the balloon wall.
In another aspect, the invention provides a controlled cryosurgical method comprising positioning a balloon within a diseased portion of a blood vessel. The balloon is inflated with an inflation fluid having a predetermined phase change temperature. The diseased portion of the blood vessel is cooled by cryogenically cooling the inflation fluid to the predetermined phase change temperature. Preferably, the predetermined phase change temperature limits a minimum temperature of the diseased vessel wall to between about xe2x88x925xc2x0 C. and xe2x88x9215xc2x0 C.
In another aspect, the present invention provides a system for treatment of a blood vessel having a diseased vessel wall. The system comprises a catheter body having a proximal end and a distal end and defining an axis therebetween. At least one balloon is disposed at the distal end of the body so that the at least one balloon can be positioned within the blood vessel adjacent the diseased vessel wall. The at least one balloon has an outer surface, and an angioplasty pressurization system is coupled to the proximal end of the body for balloon distention of the diseased vessel wall. A cooling fluid system is coupled to the proximal end of the body for cooling the diseased vessel wall. Thermal insulation is disposed between the cooling system and the outer surface of the balloon so as to limit cooling of the diseased vessel wall.
The thermal insulation may comprise a composition having a predetermined phase change temperature, as described above. Alternatively, the insulation may comprise a coating of a suitable material disposed on an inner or outer surface of the balloon, ideally being disposed between two nested balloon walls. Suitable insulation materials include expanded Teflon(trademark) (ePTFE). Typically, both an angioplasty balloon and a cryogenic balloon will be included near the distal end of the catheter body, so that the characteristics of these two different structures can be optimized for their intended use. The catheter body generally includes an angioplasty lumen and one or more cryogenic fluid lumens to provide fluid communication between the pressurization and cooling systems and their associated balloon structures. In some embodiments, the balloons may be nested one inside the other (the cryogenic balloon preferably being disposed within the angioplasty balloon). Dilation may then be effected as with a standard angioplasty system, for example, by inflating the angioplasty balloon with a high contrast liquid. Cryogenic cooling of the vessel wall at the site of dilation may be performed before, during, and/or after expanding the vessel by introducing a cryogenic cooling fluid through the catheter body and into the nested cryogenic balloon. Optionally, the high contrast liquid within the angioplasty balloon may be at least partially evacuated during inflation of the nested cryogenic balloon, making it easier for the cryogenic fluid to inflate the cooling balloon and enhancing thermal coupling between the cooling fluid and the diseased vessel wall. Advantageously, the surrounding angioplasty balloon also acts as a safety mechanism, containing any exhaust gases which might escape from the cryogenic balloon. In an alternative embodiment, the angioplasty and cryogenic balloons may be axially displaced from each other.
In yet another aspect, the invention provides a system for treatment of a blood vessel having a diseased vessel wall. The system comprises a catheter body having a proximal end and a distal end and defining an axis therebetween. An angioplasty balloon is disposed at a first axial position on the body for positioning within the blood vessel adjacent the diseased vessel wall. A cryogenic balloon is disposed at a second axial position on the body.
In another aspect, the invention provides a system for treatment of a blood vessel having a diseased vessel wall. The system comprises a catheter body having a proximal end and a distal end and defining an axis therebetween. At least one balloon is disposed at the distal end of the body for positioning within the blood vessel adjacent the diseased vessel wall. An angioplasty pressurization system is coupled to the proximal end of the body for balloon distention of the diseased vessel wall. A cooling fluid system is coupled to the proximal end of the body for cooling the diseased vessel wall. A controller is operatively coupled to at least one of the pressurization system and the cooling system so as to coordinate distention of the diseased vessel wall with cooling of the diseased vessel wall.
In another aspect, the invention provides a catheter for treatment of a blood vessel having a diseased vessel wall. The catheter comprises a catheter body having a proximal end and a distal end. The body contains an angioplasty pressurization lumen, a cryogenic fluid supply lumen, and a cryogenic fluid exhaust lumen. An angioplasty balloon is disposed near the distal end of the body. The angioplasty balloon is in fluid communication with the pressurization lumen, and is capable of dilating the diseased vessel wall when the angioplasty balloon is pressurized within the blood vessel. A cryogenic balloon is also disposed near the distal end of the body. The cryogenic balloon is in fluid communication with the exhaust lumen. A diffuser having a plurality of cryogenic fluid ports is disposed within the cryogenic balloon. The supply lumen is in fluid communication with the balloon through the diffuser so that cryogenic fluid from the supply lumen is distributed within the balloon by the diffuser.
In each of these devices, systems, and methods, a stent may optionally be placed over the balloon so that the stent can be deployed within the body lumen. Cooling may be effected before or during deployment of the stent, and will preferably be effected after the stent is deployed using the balloon.